Surface acoustic wave filter having a continuous electrode for connection of multiple bond wires

ABSTRACT

In A surface acoustic wave filter constituted with a ladder of resonators having a resonance frequency or an anti-resonance frequency, an input current flowing into a resonator in a parallel arm at the first stage from the input is so large as to deteriorate its lifetime caused from a heat generation by the resistance of the thin film wiring. As a measure to this problem, bonding wires ( 30, 31 ) connected onto points on connection electrodes ( 130, 131 ) for connecting an end of each of plural comb teeth electrodes  111  forming the resonators R s1  &amp; R p1 , or on a lead conductor ( 103 - 1 ) extended longitudinally from the connection electrode, are allotted at both sides of a center line (C 1 ) of the plural comb teeth electrode group. Furthermore, a bonding wire may be connected substantially onto the center line C 1  as well. It is preferable for the bonding wires to be located substantially symmetric with respect to the center line C 1 . It is preferable that the width along the longitudinal direction of the comb teeth electrodes is lager than a width of the comb teeth electrode.

This application is a divisional application of U.S. patent applicationSer. No. 08/640,948 filed May 15, 1996 now U.S. Pat. No. 5,955,933,which is a 371 of International Application No. PCT/JP95/02293, filedNov. 10, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave filter of aladder type, especially to an improvement of its power-withstandingcharacteristics.

2. Description of the Related Art

Recently, the market of mobile communication apparatus represented by,for example, portable telephones are rapidly expanding, and the demandfor small and efficient parts to be used in these apparatus has becomestrong. Because the high power-withstanding characteristic is requiredin an antenna switch located in a front end of radio frequency circuitof the mobile communication terminal, there has been conventionallyemployed a dielectric filter. However, in order to make the apparatusfurther smaller it is necessary to replace the dielectric filter with asurface acoustic wave (referred to hereinafter as a SAW) filter. On theother hand, width of electrodes of the SAW filter becomes minute as theoperation frequency rises; accordingly, further power-withstandingcharacteristic has come to be required.

The SAW filter of a ladder type is a filter in which SAW resonatorshaving mutually different resonance characteristics (single-pairterminal resonator) are arranged in the parallel arm and in the seriesarm, where insertion loss can be decreased very much owing to the use ofthis ladder type SAW filter compared with the case using a SAW filter ofa transversal type in which the comb teeth electrode pair is connectedin multiple stages. Details of the SAW resonator will be explainedlater.

Impedance of the resonator is zero at the resonance frequency fr, and ismaximum at the antiresonance frequency fa. On the contrary, theadmittance is maximum at the resonance frequency fr, and is zero at theantiresonance frequency fa. That is, the resonator is tuned in two ways.

Such resonators are connected in an L shape arrangement so as toconstitute a two-pair terminal resonator, where the resonance frequencyof resonator Rp in the parallel arm and resonator Rs in the series armare set such that the antiresonance frequency faP of resonator Rp of theparallel arm conforms substantially to the resonance frequency frs ofresonator Rs in the series arm, Whereby, there is formed a band-passfilter having a center frequency which is the resonance frequency frs ofresonator Rs in the series arm. Then, a band-pass filter characteristicwhich satisfies the specification, such as of portable telephones, isaccomplished by connecting the two-pair terminal resonators in multiplestages to form a ladder structure as shown in an equivalent circuit ofFIG. 3A.

When the SAW filter is built in a radio frequency circuit, such as ofportable telephones, an electric power withstanding characteristic isrequired corresponding to the maximum transmitting power of theapparatus. A consideration to Joule heat is severely required,particularly in the use in an antenna duplexer (a transmitter/receiverswitch) to which the transmitting power output from the output amplifierstage is applied. The antenna duplexer is a device for sharing theantenna by transmitter and receiver by the utilization of the differencebetween the transmitting frequency and the receiving frequency, andconsists of a transmitter band-pass filter in which the transmittingfrequency band is in the pass-band and a receiver band-pass filter inwhich the receiving frequency band is in the pass-band.

In the prior art SAW filter, there was a problem in that the temperaturerose in the filter chip which formed the resonator and thecharacteristic was apt to deteriorate when a signal was input at anattenuation band (a stop band) which is at the lower frequency side inthe filter characteristic (bandpass characteristic). That is,power-withstanding characteristics at the attenuation band at the lowerfrequency side was low compared with power withstanding characteristicsat other frequency bands.

Therefore, when an antenna duplexer employed in, for instance, AMPS(Automatic Message Processing System), which is an analog portabletelephone system, adopted in North America and South America, wascomposed of a prior art SAW filter, the receiver filter, to which thesignal of the frequency band (transmitting signal) having lowpower-withstanding characteristics was input, was deteriorated earlierthan the transmitting filter, because the transmitting frequency(824-849 MHz) is lower than the receiving frequency (869-894 MHz).

On the other hand, the current route varies depending on the inputsignal frequency as shown in FIG. 2, which schematically illustrates therelation between the filter characteristic and the current routes in theSAW filter. That is, in principle, the signal current of the frequencyof pass band A flows in the series arm, and the signal current of thefrequency of attenuation band B1 at the lower frequency side flowschiefly in the parallel arm. The signal at the high frequency sideattenuation band B2 hardly flows into any resonator in the filter.

Moreover, when the currents in each stage are compared in the laddertype filter, the currents become smaller in the order going from thefirst stage at the input side to the latter stage. That is, therelations are expressed by formulas (1) and (2), where the currentsflowing in each resonator RS1, RS2, Rp1, Rp2 and Rp3 are Is1, Is2, Ip1,Ip2, and Ip3, respectively, as shown in FIG. 3A.

Is1>Is2  (1)

Ip1>Ip2>Ip3  (2)

Therefore, it is considered that the decrease in the Joule heat causedfrom the current Ip1 flowing in resonator Rp1 of the parallel arm at theinput side first stage is especially effective in improving the powerwithstanding characteristics of attenuation band B1 at the lowerfrequency side.

Here, impedance Z of resonator Rp1 is represented by formula (4)according to FIG. 3(B).

Z=Z1*Z2/(Z1+Z2)  (4)

where Z1=−j/ωC₀ and

Z2=R+jωL−j/ωC₁

And, resistance element Zr (real part of impedance Z) involved in theJoule heat is shown by the formula (5).

Zr=R/(ωC ₀)² [R ²+(ωL−1/ωC ₀−1/ωC₁)²]  (5)

In resistance element Zr, resistance R can be decreased by appropriatelyselecting opening width x of comb teeth electrodes 111 shown in FIG. 1and the number of the pairs (Japanese Provisional Patent PublicationHEI6-29779).

However, it was confirmed by the present inventors that the resistanceof the wiring conductor formed with a thin film largely took part in theheating of the filter chip according to the below-described experiments.

In the parallel arm of the input side first stage, actual resistanceelement ZR1 which contributes to the heating of the filter chip isrepresented by formula (6). R1 in formula (6) is resistance of the partbetween the resonator and the bonding wire in the above-mentioned wiringconductor.

ZR1=Zr+R1  (6)

DISCLOSURE OF THE INVENTION

The present invention is derived from the above-mentioned consideration,and aims at enhancing of the reliability of the present SAW filterresulted from the reduction of the heat generation at a thin filmconductor between a resonator and a bonding wire, particularly of aresonator in the parallel arm at the input stage, so as to suppress thetemperature rise of the resonator whereby its power-withstandingcharacteristics is improved.

In the surface acoustic wave filter constituted with a ladder ofresonators having a resonance frequency or an anti-resonance frequency,bonding wires (30, 31) are connected to positions on connectionelectrodes for connecting an end of each of plural comb teeth electrodes111 forming the resonators R_(s1) & R_(p1), or to a lead conductorextended longitudinally from the connection electrode, where thepositions are allotted at both sides of a center line C1 of the pluralcomb teeth electrode group. The bonding wire may be further connectedsubstantially onto the center line C1, too. It is preferable that thebonding wires are located substantially symmetric with respect to thecenter line C1. It is preferable that a width b, along the longitudinaldirection of the comb teeth electrode, of the connection electrode 130,131 is larger than a width w of the comb teeth electrode. Or, a bondingwires 33′ is connected onto a point within the length L of theconnection electrode 130′ at the ground side of the resonator,preferably onto a point in the vicinity of the center line c1. Leadconductors 130-1 may be extended longitudinally from both ends of theconnection electrode.

Moreover, plural projections 130-3 are projected from the connectionelectrode in a direction opposite from the comb teeth electrodes, atpoints on the connection electrode or on the lead conductor 130-1extending longitudinally from the connection electrode, where the pointsare allotted on both the sides of the center line, and the bonding wires33′ are connected onto the projections 130-3, respectively. A space130-4 between the projections 130-3 may be filled with an electricallyconductive material. The above-mentioned bonding wire connectingstructure can be applied solely to a SAW resonator.

Or, the thickness of the connection electrodes 130, 130′ and 131together with its lead conductor 130-1 is formed thicker than thethickness of the comb teeth electrodes.

In each parallel arm the electrical resistance of the connectionelectrode itself and the electrical resistance on the way to the bondingwire are reduced so as to suppress Joule heat generation, wherebytemperature rise of the resonator is suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plane view showing the structure of the SAW resonator;

FIG. 2 schematically illustrates the relation between the filtercharacteristic and the current route;

FIGS. 3A and 3B show an equivalent circuit of the SAW filter andresonator;

FIG. 4 is a plane view of the first preferred embodiment of the SAWfilter of the present invention;

FIG. 5 is a plane view of the second preferred embodiment of the SAWfilter of the present invention;

FIGS. 6A, 6B, 6C, 6D, 6E and 6F show figures of the samples in which thepositions of the bonding wires to be connected to are varied;

FIGS. 7A and 7B show the temperature and the value of the withstandingpower of the chip when the width and the thickness of connectionelectrode are varied;

FIG. 8 shows comparison data of the lifetime when the signal input levelis varied;

FIG. 9 shows a plane view of the third preferred embodiment of thepresent invention showing a variation example of the leading out methodof the bonding wires;

FIG. 10 shows a cross-sectional view of the fourth referred embodimentof the present invention where the thickness of the connection electrodeis varied; and

FIG. 11 is a plane view of the fifth preferred embodiment of the presentinvention where the number of the bonding wire is chosen one.

THE BEST MODE TO EMBODY THE INVENTION

In FIG. 1 is shown a plane view of an example of an electrode structureused commonly for SAW resonator Rp and Rs in the parallel arm and theseries arm of the ladder type structure.

The SAW resonator (referred to hereinafter simply as resonator) isconstituted with a plurality of comb teeth electrodes 111 inserted intobetween a plurality of comb teeth electrodes opposed thereto so as toform a pair, an exciter part to connect the comb teeth electrodes' openends with connection electrode 130, and reflectors 120 arranged on boththe sides of the above-mentioned comb teeth electrode pairs along thedirection of propagation of the surface acoustic wave. Theabove-mentioned excitation part becomes an input/output terminal for theexcitation as well as the reception. The reflector of the example inFIG. 1 is formed with a plurality of comb teeth electrodes where theopen ends are mutually short-circuited. The comb teeth electrodes orstrip array electrodes, each of an open end type, can be employed as thereflector. Though the reflector is drawn to be electrically connected tothe exciter part with 1 lead conductor 130-1, the reflector may becomposed without the connection on demand from the characteristic designof the filter.

Conductor patterns of each resonator RS1, RS2 and Rp1 to Rp3, which arecomb teeth electrodes and reflectors, and other wiring conductorsconsist of a thin film conductor of three-layer structure of Al-2%Cu(125nm)/Cu(45 nm)/Al-2%Cu(125 nm). Resonators RS1, RS2 and Rp1 to Rp3 aredesigned to meet the specification of the receiver filter of AMPS(AMPS-Rx: receiving band 869-894 MHz).

SAW filter 1 is composed of a package 10 made of ceramic of aboutseveral milli-meter square, a filter chip 20 bonded to the inner surfaceof the bottom 10A of package 10, bonding wires 31 to 35, etc. whichconsist of Au wire or Al wire of, for instance 25 μmφ as shown in FIG.4.

Package 10 is provided with bonding tables 10C along two opposed sidesin frame sidewall 10B. Upon the surfaces of the bonding tables 10C areprovided external connection terminals T1 to T3 which consist of Aufilms, for example.

Filter chip 20 is such that a thin film conductor of a predeterminedpattern, which will be separately explained later, is provided on asingle-crystal substrate of 36° rotation, Y-cut, X-propagation LiTaO3(tantalic acid lithium), and is made according to a conventionally knownprocess.

In filter chip 20 are formed two resonators RS1 & RS2 which are thestructural elements of the series arm, and three resonators Rp1, Rp2 &Rp3 which are the structural elements of the parallel arms in the laddertype filter, and predetermined wiring conductors including the bondingpad. Totally five resonators RS1, RS2 and Rp1 to Rp3 are arranged so asto shift mutually in the vertical direction of FIG. 4 so that thepropagation path of each surface acoustic wave should not mutuallyinterfere.

In the resonator shown in FIG. 1, width w of the comb teeth electrodesin the exciter part is about 1.2 μm, length is about 81 μm, and thenumber of comb teeth is 58 pairs.

Connection electrodes 130 for connecting the comb teeth electrodes havea width to connect all the comb teeth electrodes for the excitation,that is, a length L (L′) in the direction of the SAW propagation, andhave a width b in the direction of length of comb teeth, that is in itsright-angled direction. The length L (L′) is about 278 μm, the width bis about 80 μm, and the thickness is about 300 nm as mentioned above.The value b of the width is large enough compared with width w of thecomb teeth.

Resonator Rp1 of the parallel arm on the input side has a structureshown in FIG. 1, where pads 130-2 are provided respectively at open endsof lead conductor 130-1 along the direction of the length of theconnection electrode 130, that is, in direction of the array of the combteeth electrode group 111 as shown in FIG. 4; and thereon arerespectively connected bonding wires 33 by a method of widely usedsupersonic wave, etc. so as to connect to ground terminals T3. That is,they are connected to two points allotted by a center line C1 of theexciter. Connection conductor 131 is connected as well on the inputexciter side of resonator Rp1 of a parallel arm similarly to conductor130, where lead conductor 131-1 having its entire length as the width ofthe exciter part extends to connection electrode 131-2 of an input stageresonators RS1 of the series arm. Two bonding wires 31 are connected tothe points, allotted by center line C1 of the resonator, on this leadconductor 131-1 so as to connect to signal input terminal T1.

The output side of resonator RS1 of the input stage of the series arm,the input side of resonator RS2 of the series arm of the second stage,and the input sides of resonator Rp2 of a parallel arm of the secondstage are mutually connected by thin film wiring 132. Each resonator isprovided with a connection electrode for connecting thin film wiring 132to each resonator in the similar way to connection electrode 130;however, they are not particularly shown in the figure. Connectionelectrode 133 is provided on the ground side of resonator Rp2 of theparallel arm of the second stage similarly to connection electrode 130,and two bonding wires 34 are welded at the points allotted by a centerline of connection electrode so as to connect to ground terminal T3similarly to connection electrode 130. The ground side of resonator Rp3of the parallel arm of the third stage is connected to ground terminalT3 via two bonding wires 35 similarly to the connection of connectionelectrode 130, lead conductor 130-1 and pad 130-2.

It was explained that the locations of two bonding wires 33 welded onground sides of resonator Rp1 of the input side first stage wereallotted to both the sides of center line C1 in the direction of lengthL of connection electrode 130. However, in order to decrease electricalresistance it is further preferable that the welding points are locatedat symmetric positions with respect to center line c1 of connectionelectrode 130 of resonator Rp1, that is, apart at substantially equaldistances in mutually opposite directions.

In order to confirm the problem of the above-mentioned prior arttechnology and to confirm the effect of the structure of the invention,there were made six kinds of samples 1A to 1F in which the bondingpositions were varied as shown in FIG. 6A to FIG. 6F, where theconnection electrode on the ground side of resonator Rp1 of the parallelarm of the input stage, the lead conductor connected thereto, the numberof bonding wires connected thereto, and their positions are varied. Ineach sample 1A to 1F, the bonding positions of resonators Rp2 and Rp3other than the ground side of the first stage are the same. In eachsample, the thickness of the lead conductor and connection electrode areabout 300 nm and the width is about 80 μm. Temperature and powerwithstanding characteristics were respectively measured.

The sample 1A and 1B are of the structure of prior art technology. Insamples 1A and 1B, the bonding wire is connected to an end of leadconductor 30 extended from the connection electrode of resonator Rp1.The bonding wire is one in sample 1A, and three in sample 1B.

Sample 1C to 1F are of the structure which can be embodied in thepresent invention. In sample 1C, a single bonding wire is connected oncenter line c1, that is a central part, of connection electrode ofresonator Rp1. In sample 1D, a single bonding wire is connected to bothends of resonator Rp1, respectively. The bonding positions are symmetrywith respect to center line c1. Sample 1E is of a structure almostsimilar to FIG. 4. Lead conductor 130-1 is provided to extend to boththe sides of connection electrode 130 along its longitudinal direction.Welding positions of the two bonding wires are on lead conductor 130-1respectively substantially 150 μm outside from the edge of the combteeth electrode group.

In sample 1F, totally three bonding wires are connected one by one tothe center part and to both the ends of resonator Rp1 respectively,where the bonding positions are symmetry with respect to center line c1.

These samples 1A to 1F were placed in a thermostatic oven, where theenvironmental temperature was kept at 85° C., and a constant power (forinstance, an initial value 1 W) was applied thereto while changing thefrequency by 1 MHz within the range of 340 to 930 MHz. Afterwards, thefilter characteristic was measured after the power application had beenterminated. If there was no characteristic deterioration, the appliedelectric power was further incremented by 0.1 W so as to carry out thesame measurements. Applied power at which the deterioration of thefilter characteristic became remarkable as described below was definedas the value of the withstanding power. That is, the applied electricpower at which the decrease in the band width of the pass band reached 2MHz or deterioration in the attenuation pole of the low frequency sidereached 5 dB was defined as the value of the withstanding power.

Concurrently to the measurement of the filter characteristic wasmeasured the temperature of filter chip 20 (chip temperature) byconverting the resistance value of a conductor pattern of a miandaprovided in the neighborhood of resonator Rp1 into a temperature value.

Values of the withstanding power of each sample 1A to 1F, real part ZR1of the impedance of the parallel arm at the frequency at the attenuationpole of the low frequency side, and the temperature of the chip (with1.3 W input) are collectively shown in Table 1.

TABLE 1 Real Part of Chip Temp. Withstand Sample the Imped. [Ω] [° C.]Power [W] 1A 5.67 123.6 1.4 1B 5.68 137.5 1.4 1C 2.43 106.0 1.8 1D 2.71104.0 2.1 1E 3.10 110.8 1.9 1F 2.14 99.6 2.0

As apparent from Table 1, when the bonding position was located oncenter line c1 of resonator Rp1, on both sides of center line c1, or onand on both the sides of center line c1 (sample 1C to 1F), the real partof impedance which causes Joule heat was small, whereby the temperaturerise of the chip was suppressed. Accordingly, the power withstandingcharacteristics were raised. Moreover, it was confirmed as a result ofan analysis employing a Smith chart, which is not shown in the figure,that the reflection coefficients were increased at the attenuation bandso that the interference between the filter characteristics for thetransmitting and for the receiving was reduced when used in the antennaduplexer.

Though input and output terminals of the signal are connectedrespectively via two bonding wires 31 and 32 to signal input terminal T1or signal output terminal T2 in the first preferred embodiment shown inFIG. 4, a single bonding wire is connected here respectively, so that acomparison examination was actually done to the sample of the structureof prior art, which is not shown in the figure, having a 10 μm width bof the connection electrode and a 70-80 μm width of lead conductor131-1. As a result, when a single bonding wire 31 and 32 was connectedonto each input and output terminal the value of withstanding power was1.4 W. On the other hand, when respectively two wires were connected toeach the value of withstanding power was 1.6 W.

A second preferred embodiment is shown in FIG. 5, where the thin filmwiring conductor and the bonding wire of the first preferred embodimentare partially modified. In this preferred embodiment, a single bondingwire 31′ is connected from input terminal T1 substantially onto thecenter of lead conductor 131-1 of the resonator input side. Leadconductor 131-1 is connected with connection electrodes 131 and 131-2 ofthe parallel and series resonators Rp1 and RS1, respectively. The widthof connection electrode 131 is as wide as 20 μm and the width in thedirection of length of connection electrode 131 is 100 μm, whichoccupies about ⅓ of the width of the comb teeth group. Therefore, thecurrent from the connection point of the bonding wire to the comb teethelectrodes is distributed enough, that is, the electrical resistance islow enough.

The structures of the samples 1C, 1D and 1F shown in FIG. 6 are notparticularly explained as an independent preferred embodiment; however,because of its clear effect it is needless to say that they can beapplied to the lead conductor of the resonator according to the conceptand the proof data of the present invention.

Moreover, data in variation of width b and thickness h of the connectionelectrode, that is, of the electrical resistance, is shown in FIG. 7Aand FIG. 7B in order to confirm the temperature rise of the chip and thepower withstanding characteristics. This data was measured on theabove-mentioned sample 1A. It is seen that an increase in width b and hin thickness of the connection electrode contributes to the decrease inthe temperature rise of the chip as seen from this figure.

The result of life tests of the filter of the above-mentioned firstpreferred embodiment and the filter of the prior art technology whichuses above-mentioned sample 1B on the earth side of the parallelresonator on the input side is shown in curves a and b of FIG. 8. Thehorizontal axis of the figure shows the input signal power level. Lifetests were carried out respectively on three to four kinds of inputsignal power levels at the environmental temperature 35° C. as shown inthe figure. The input signal frequency is a frequency in the attenuationpole at the lower frequency side of the filter. Judgment of the lifetime was the same as the condition of the case of Table 1. The lineplotted in this figure is extended until intersecting with the 1 W linewhich is a practical input signal power level, then it was found thatthe lifetime of the prior art structure was 69,000 hours, and thelifetime of the present invention structure was 24,000,000 hours; thusit was proven that the effect of the present invention was remarkable.

In the above-mentioned preferred embodiment, the bonding wires wereconnected onto the connection electrode and onto the lead conductorextended in its longitudinal direction. However, in FIG. 9 is shown asthe third preferred embodiment a case where three lead conductors 130-3are provided in a pad shape projected from a side of the connectionelectrode opposite to the comb teeth electrodes, and the bonding wiresare connected thereto, respectively. In this case, width b of theconnection electrode need not necessarily be larger than width w of thecomb teeth electrode, and is determined by the shape, the number of leadconductors 130-3, and the thickness, etc. of the connection electrode.It is needless to say that the part 130-4 between pads shown with thedotted line is allowed to be buried though only the portion of the padis projected from the connection electrode in FIG. 9.

Though the area was enlarged as a means for decreasing the electricalresistance the connection electrode in the above-mentioned preferredembodiment, and the welding positions were selected so as to distributethe current in the connection electrode, otherwise is possible to copetherewith by increasing the thickness of the connection electrode aswell. This is shown in FIG. 10 as the fourth preferred embodiment. Thisfigure shows a cross-sectional view cut along a comb teeth electrode.The thickness of the connection electrode is 1200 nm while the thicknessof the comb teeth electrodes is 300 nm. The number of the bonding wiresconnected onto the connection electrode is chosen according to thepreferred embodiment mentioned above. The effect thereof was describedin FIG. 7A and FIG. 7B. Lead conductors may be led out from theconnection electrode so that the bonding wires be connected onto thelead conductors. Moreover, the lead conductor may be formed as thick asthe connection electrode. The increase of the thickness is performed byadding the patterning process utilizing a lithography method.

In FIG. 11 is shown, as the fifth preferred embodiment, a case where asingle bonding wire is used at the ground side of the parallel resonatorof the input stage. The all except the bonding wire 33″ are the same asthe second preferred embodiment shown in FIG. 5. Bonding wire 33″ isconnected onto substantially the central part of connection electrode130-1. The heat generation is a little as well as the reliability isenough, because width b of connection electrode 130-1 is wide enough as30 μm as explained previously. The advantage of this structure is inthat the number of bonding wires is small. The bonding wires led outrespectively from both the sides of electrode 130-1 in the firstpreferred embodiment have also a purpose of avoiding an interferencewith input bonding wire 33. However, there is, in the fifth preferredembodiment, also a characteristic effect of covering the surface of thechip with a thin film electrode.

Though there was shown the case where the number of bonding wires wasone or two in the above-mentioned preferred embodiment, it is needlessto say that the use of three or more bonding wires may be used accordingto the concept of the present invention. In that case, it is preferableto connect the middle one onto the vicinity of center line c1.

The structure of the filter chip, length and position of the number ofbonding wire can be determined while adjusting inductance L1 to L3 shownin the FIG. 3A by suitably selecting the number and the length of thebonding wires to the desirable value and considering the improvement ofthe filter characteristic at the same time. (Japanese Provisional PatentPublication, No. HEI5-183380, and Japanese Provisional PatentPublication, No. (HEI6-164309).

Moreover, the number of the stages of the ladder, the electrode patternof each resonator, the arrangement relation of each resonator, the planepattern of the wiring conductor, the material and thickness of the thinfilm conductor of the filter chip, and the material of the piezoelectric substrate, the structure of the package, the arrangementrelation of each terminal T1-3 to filter chip 20, and the material andsizes of bonding wires 31 to 35, etc. can be variously modified.

Because, as previously explained, except in the input/output circuit ofparallel arm resonator Rp1 at the input stage, the current value is lowcompared with resonator Rp1, neither of the welding position nor thewiring form of the bonding wire is severe compared with those inparallel arm resonator Rp1 at the input stage. Which form of theabove-mentioned preferred embodiments is to be chosen, that is, theposition and the number of bonding wires, is often determined accordingto an overall judgment on the problem of the adjustment of inductanceand the interference with other bonding wires, etc.

It is needless to say that the present invention can be applied to amere SAW resonator though there was presented in the above-mentionedpreferred embodiments the cases where the present invention was appliedto SAW filters.

As described above, according to the present invention the heatgeneration at between the resonator and the bonding wire is reduced sothat the temperature rise of the resonator is suppressed; accordingly,the improvements of the power-withstanding characteristics as well asthe lifetime can be accomplished, without considerably affecting thefilter characteristics of the resonators.

What is claimed is:
 1. A surface acoustic wave filter comprising: aplurality of parallel arms including a first resonator having a firstresonance characteristic and a series arm including a second resonatorhaving a second resonance characteristic having a resonance frequencywhich is substantially equal to an anti-resonance frequency of saidfirst resonators, wherein an input resonator of one of said firstresonators of said parallel arm is connected to an input of said surfaceacoustic wave filter, at least said input resonator including aplurality of comb teeth electrodes each of which has opposing first andsecond ends, at least a continuous connection electrode directlyconnecting the first end of each of said plurality of comb teethelectrodes while the second end of each of said plurality of comb teethelectrodes remains electrically open such that each of said plurality ofcomb teeth electrodes is arranged perpendicular to said continuousconnection electrode, and bonding wires connected to said continuousconnection electrode at both sides of a center line of said plurality ofcomb teeth electrodes.
 2. A surface acoustic wave filter as recited inclaim 1, wherein said connection electrode is provided on a groundingside of said input resonator.
 3. A surface acoustic wave filter asrecited in claim 1, wherein said connection electrode is provided at aninput side of said input resonator.
 4. A surface acoustic wave filter asrecited in claim 1, wherein a width b, along the longitudinal directionof said comb teeth electrode, of said continuous connection electrode islarger than a width w of said comb teeth electrode.
 5. A surfaceacoustic wave filter as recited in claim 1, further comprising a leadconductor connected to said connection electrode, wherein said bondingwires are connected onto said lead conductor extending along alongitudinal direction of said continuous connection electrode.
 6. Thesurface acoustic wave filter as recited in claim 1, wherein each of saidfirst resonators include first and second groups of comb teethelectrodes, a first connection electrode electrically connecting saidfirst group of comb teeth electrodes, and a second connection electrodeelectrically connecting said second group of comb teeth electrodes; andsaid center line of said input resonator of said first resonatorsdivides both of said first and second groups of comb teeth electrodes sothat an equal number of comb teeth electrodes lie on either side of saidcenter line.
 7. A surface acoustic wave device comprising: a firstresonator, including a first plurality of comb teeth electrodes, asecond plurality of comb teeth electrodes, comb teeth electrodes of saidfirst and second plurality of comb teeth electrodes extending in alengthwise direction and arranged alternately in an interleaving mannerin a widthwise direction, a first continuous connection electrodeconnected directly to each of said first plurality of comb teethelectrodes on a first side of said first plurality of comb teethelectrodes, a second continuous connection electrode connected directlyto each of said second plurality of comb teeth electrodes on a secondside of said second plurality of comb teeth electrodes, opposite saidfirst side, and a pair of reflectors arranged at ends of said first andsecond plurality of comb teeth electrodes, wherein at least one of saidfirst and second continuous connection electrodes extends beyond atleast one of opposite ends of a corresponding one of said first andsecond plurality of comb teeth electrodes and extends up to but notalongside said pair of reflectors, wherein said first and secondcontinuous connection electrodes have such a width in a directionparallel to the lengthwise direction of each of said first and secondplurality of comb teeth electrodes at any place between opposite ends ofeach of said first and second continuous electrodes in a lengthwisedirection that a bonding wire is connectable to a corresponding one ofsaid first and second continuous electrodes.
 8. The surface acousticwave device of claim 7, wherein at least a bonding wire is connected toone of said first and second continuous electrodes substantially on acenter line of said first and second plurality of comb teeth electrodes,the center line extending in a direction substantially parallel to thelengthwise direction of electrodes of said first and second plurality ofcomb teeth electrodes.
 9. A surface acoustic wave device comprising: afirst resonator, including a first plurality of comb teeth electrodes, asecond plurality of comb teeth electrodes, comb teeth electrodes of saidfirst and second plurality of comb teeth electrodes extending in alengthwise direction and arranged alternately in an interleaving mannerin a widthwise direction, a first continuous connection electrodeconnected directly to each of said first plurality of comb teethelectrodes on a first side of said first plurality of comb teethelectrodes, a second continuous connection electrode connected directlyto each of said second plurality of comb teeth electrodes on a secondside of said second plurality of comb teeth electrodes, opposite saidfirst side, wherein at least one of said first and second continuousconnection electrodes extends in a lengthwise direction beyond at leastone of opposite ends of a corresponding one of said first and secondplurality of comb teeth electrodes, wherein said first and secondcontinuous connection electrodes have such a width in a directionparallel to the lengthwise direction of each of said first and secondplurality of comb teeth electrodes at any place between opposite ends ofeach of said first and second continuous electrodes in a lengthwisedirection that a bonding wire is connectable to a corresponding one ofsaid first and second continuous electrodes, and wherein at least firstand second bonding wires having first ends are connected to one of saidfirst and second continuous connection electrodes at opposite sides of acenter line of said first and second plurality of comb teeth electrodes,the center line extending in a direction substantially parallel to thelengthwise direction of electrodes of said first and second plurality ofcomb teeth electrodes.
 10. The surface acoustic wave device of claim 9,wherein each of the first and second bonding wires is connected to oneof said first and second continuous connection electrodes at a placeinside opposite ends of said first and second plurality of comb teethelectrodes in the widthwise direction.
 11. The surface acoustic wavedevice of claim 9, wherein each of the first and second bonding wires isconnected to the one of said first and second continuous connectionelectrodes at a place outside opposite ends of said first and secondplurality of comb teeth electrodes in the widthwise direction.
 12. Thesurface acoustic wave device of claim 9, wherein at least a bonding wireis connected to the corresponding one of said first and secondcontinuous electrodes by jumping over said first and second plurality ofcomb teeth electrodes in a lengthwise direction of said comb teethelectrodes.
 13. A surface acoustic wave device comprising: a firstresonator, including a first plurality of comb teeth electrodes, asecond plurality of comb teeth electrodes, comb teeth electrodes of saidfirst and second plurality of comb teeth electrodes extending in alengthwise direction and arranged alternately in an interleaving mannerin a widthwise direction, a first continuous connection electrodeconnected directly to each of said first plurality of comb teethelectrodes on a first side of said comb teeth electrodes, a secondcontinuous connection electrode connected directly to each of saidsecond plurality of comb teeth electrodes on a second side of said combteeth electrodes, opposite to said first side, at least first and secondbonding wires having first ends connected to said continuous firstconnection electrode at opposite sides of a center line of saidplurality of comb teeth electrodes, the center line extending in adirection substantially parallel to the lengthwise direction ofelectrodes of said first and second plurality of comb teeth electrodes;and a common external electrode, wherein said first continuousconnection electrode does not extend beyond said first plurality of combteeth electrodes and said second continuous connection electrode doesnot extend beyond said second plurality of comb teeth electrodes, andwherein second ends of said first and second bonding wires are connectedto said common external electrode.
 14. The surface acoustic wave deviceof claim 13, wherein said common external electrode is an input of saidsurface acoustic wave device.
 15. The surface acoustic wave device ofclaim 13, wherein said common external electrode is grounded.
 16. Asurface acoustic wave filter comprising: a plurality of parallel armseach including a first resonator having a first resonance characteristicand a plurality of series arms each connected between each of saidparallel arms including a second resonator having a second resonancecharacteristic having a resonance frequency which is substantially equalto an anti-resonance frequency of said first resonators, wherein one ofsaid second resonators of said plurality of series arms is connected toan input of said surface acoustic wave filter and to an input resonator,at least said input resonator including a plurality of comb teethelectrodes each of which has opposing first and second ends, at least acontinuous connection electrode directly connecting the first end ofeach of said plurality of comb teeth electrodes while the second end ofeach of said plurality of comb teeth electrodes remains electricallyopen such that each of said plurality of comb teeth electrodes isarranged perpendicular to said continuous connection electrode, andbonding wires connected to said continuous connection electrode at bothsides of a center line of said plurality of comb teeth electrodes.
 17. Asurface acoustic wave device comprising: a first resonator, including afirst plurality of comb teeth electrodes, a second plurality of combteeth electrodes, comb teeth electrodes of said first and secondplurality of comb teeth electrodes extending in a lengthwise directionand arranged alternately in an interleaving manner in a widthwisedirection, a first continuous connection electrode connected directly toeach of said first plurality of comb teeth electrodes on a first side ofsaid comb teeth electrodes, a second continuous connection electrodeconnected directly to each of said second plurality of comb teethelectrodes on a second side of said comb teeth electrodes, opposite tosaid first side, and at least first and second bonding wires havingfirst ends connected to said continuous first connection electrode atopposite sides of a center line of said plurality of comb teethelectrodes, the center line extending in a direction substantiallyparallel to the lengthwise direction of electrodes of said first andsecond plurality of comb teeth electrodes, wherein said first continuousconnection electrode does not extend beyond said first plurality of combteeth electrodes and said second continuous connection electrode doesnot extend beyond said second plurality of comb teeth electrodes,wherein said first and second bonding wires have second ends connectedto an input of said surface acoustic wave device.
 18. A surface acousticwave device comprising: a plurality of resonators connected in parallelincluding a first resonator, which includes: a first plurality of combteeth electrodes, a second plurality of comb teeth electrodes, combteeth electrodes of said first and second plurality of comb teethelectrodes extending in a lengthwise direction and arranged alternatelyin an interleaving manner in a widthwise direction, a first continuousconnection electrode connected directly to each of said first pluralityof comb teeth electrodes on a first side of said comb teeth electrodes,a second continuous connection electrode connected directly to each ofsaid second plurality of comb teeth electrodes on a second side of saidcomb teeth electrodes, opposite to said first side, and at least firstand second bonding wires having first ends connected to said continuousfirst connection electrode at opposite sides of a center line of saidplurality of comb teeth electrodes, the center line extending in adirection substantially parallel to the lengthwise direction ofelectrodes of said first and second plurality of comb teeth electrodes,wherein said first continuous connection electrode does not extendbeyond said first plurality of comb teeth electrodes and said secondcontinuous connection electrode does not extend beyond said secondplurality of comb teeth electrodes.
 19. A surface acoustic wave devicecomprising: a first resonator, including a first plurality of comb teethelectrodes, a second plurality of comb teeth electrodes, comb teethelectrodes of said first and second plurality of comb teeth electrodesextending in a lengthwise direction and arranged alternately in aninterleaving manner in a widthwise direction, a first continuousconnection electrode connected directly to each of said first pluralityof comb teeth electrodes on a first side of said comb teeth electrodes,a second continuous connection electrode connected directly to each ofsaid second plurality of comb teeth electrodes on a second side of saidcomb teeth electrodes, opposite to said first side, and at least firstand second bonding wires having first ends connected to said continuousfirst connection electrode at opposite sides of a center line of saidplurality of comb teeth electrodes, the center line extending in adirection substantially parallel to the lengthwise direction ofelectrodes of said first and second plurality of comb teeth electrodes,wherein said first continuous connection electrode does not extendbeyond said first plurality of comb teeth electrodes and said secondcontinuous connection electrode does not extend beyond said secondplurality of comb teeth electrodes, wherein said first and secondbonding wires are connected to said first connection electrodesymmetrical with respect to said center line.
 20. A surface acousticwave device comprising: a first resonator, including a first pluralityof comb teeth electrodes, a second plurality of comb teeth electrodes,comb teeth electrodes of said first and second plurality of comb teethelectrodes extending in a lengthwise direction and arranged alternatelyin an interleaving manner in a widthwise direction, a first continuousconnection electrode connected directly to each of said first pluralityof comb teeth electrodes on a first side of said comb teeth electrodes,a second continuous connection electrode connected directly to each ofsaid second plurality of comb teeth electrodes on a second side of saidcomb teeth electrodes, opposite to said first side, first and secondbonding wires having first ends connected to said continuous firstconnection electrode at opposite sides of a center line of saidplurality of comb teeth electrodes, the center line extending in adirection substantially parallel to the lengthwise direction ofelectrodes of said first and second plurality of comb teeth electrodes,and a third bonding wire connected to said first connection electrode,wherein said first continuous connection electrode does not extendbeyond said first plurality of comb teeth electrodes and said secondcontinuous connection electrode does not extend beyond said secondplurality of comb teeth electrodes.
 21. The surface acoustic wave deviceof claim 20, wherein said third bonding wire is connected to said firstconnection electrode at a position along said center line.
 22. A surfaceacoustic wave device comprising: a plurality of resonators connected inseries including a first resonator, which includes: a first plurality ofcomb teeth electrodes, a second plurality of comb teeth electrodes, combteeth electrodes of said first and second plurality of comb teethelectrodes extending in a lengthwise direction and arranged alternatelyin an interleaving manner in a widthwise direction, a first continuousconnection electrode connected directly to each of said first pluralityof comb teeth electrodes on a first side of said comb teeth electrodes,a second continuous connection electrode connected directly to each ofsaid second plurality of comb teeth electrodes on a second side of saidcomb teeth electrodes, opposite to said first side, and at least firstand second bonding wire having first ends connected to said continuousfirst connection electrode at opposite sides of a center line of saidplurality of comb teeth electrodes, the center line extending in adirection substantially parallel to the lengthwise direction ofelectrodes of said first and second plurality of comb teeth electrodes,wherein said first continuous connection electrode does not extendbeyond said first plurality of comb teeth electrodes and said secondcontinuous connection electrode does not extend beyond said secondplurality of comb teeth electrodes.
 23. The surface acoustic wave deviceof claim 22, wherein said first and second bonding wires have secondends connected to an input of said surface acoustic wave device.
 24. Asurface acoustic wave device comprising: a series resonator and aparallel resonator, one of which includes a first resonator, including:a first plurality of comb teeth electrodes, a second plurality of combteeth electrodes, comb teeth electrodes of said first and secondplurality of comb teeth electrodes extending in a lengthwise directionand arranged alternately in an interleaving manner in a widthwisedirection, a first continuous connection electrode connected directly toeach of said first plurality of comb teeth electrodes on a first side ofsaid comb teeth electrodes, a second continuous connection electrodeconnected directly to each of said second plurality of comb teethelectrodes on a second side of said comb teeth electrodes, opposite tosaid first side, and at least first and second bonding wires havingfirst ends connected to said continuous first connection electrode atopposite sides of a center line of said plurality of comb teethelectrodes, the center line extending in a direction substantiallyparallel to the lengthwise direction of electrodes of said first andsecond plurality of comb teeth electrodes, wherein said first continuousconnection electrode does not extend beyond said first plurality of combteeth electrodes and said second continuous connection electrode doesnot extend beyond said second plurality of comb teeth electrodes. 25.The surface acoustic wave device of claim 24, comprising: a plurality ofseries resonators connected in series between an input and an output ofsaid surface acoustic wave device, a plurality of parallel resonatorsconnected in parallel between connections of said series resonators andground, and wherein said plurality of resonators have a resonancefrequency substantially equal to an anti-resonance frequency of saidplurality of parallel resonators, and said first resonator is one ofsaid plurality of series resonators and said plurality of parallelresonators.
 26. The surface acoustic wave device of claim 25, whereinsaid first resonator is a parallel resonator of said plurality ofparallel resonators connected between the input of said surface acousticwave device and ground.
 27. The surface acoustic wave device of claim26, wherein said first and second bonding wires are connected at asecond end of said bonding wires to ground.